High quality (Q) factor inductors and capacitors are needed to achieve high performance resonant tank circuits. For example, use of high-Q resonant tank circuits can improve efficiency and lower distortion and harmonics in an RF front end and enable lower insertion losses and higher out-of-band rejections in filters and diplexers. In addition, high-Q resonant tank circuits improve RF sensitivity and selectivity.
The quality factor for an inductor or capacitor is inversely related to its direct current (DC) resistance (Rdc). While it may be relatively easy to achieve a high-Q inductor or capacitor using a discrete conventional inductor or capacitor in non-mobile applications in which space is not an issue, there is no space for such discrete components in a compact integrated design. One approach to increasing component density is thus to integrate the desired inductors and capacitors into metal layers of a package substrate. The metal layers used to form the capacitor are typically quite thin to reduce its parasitic inductance. But the interconnection between the resulting inductor and capacitor is conventionally formed in one of these relatively-thin metal layers, which increase the DC resistance and thus lowers the resulting quality factor. Alternatively, the passive components may be integrated onto the die but the metal layer thickness in modern CMOS processes is so thin that the DC resistance of the resulting passive components is also relatively high. As a result, the quality factor for die-integrated or package-integrated inductors, capacitors, and LC resonant tank circuits is limited to too low a value for the high-performance needed for RF designs.
Accordingly, there is a need in the art for integrated resonant tank circuits with improved quality factors.